Fire extinguishing sprinkler systems generally employ single operation sprinkler heads having a fusible link that melts to release a plug that normally prevents the flow of water. Once the plug is released, water is discharged from the head in a desired pattern. Such sprinkler heads must be replaced after operation and often produce extensive water damage.
In attempts to both reduce the incidence of water damage and conserve water, there have been developed many types of so-called "on-off" sprinkler heads that open in response to a fire condition and automatically close after extinguishment thereof. Typically such on-off valves utilize a temperature responsive sensor that either directly actuates a main valve member or actuates a pilot valve to create a differential pressure condition that opens a main valve member. Typical examples of such on-off sprinkler heads are disclosed in U.S. Pat. Nos. 4,128,128; 3,802,510; 3,757,866; and 3,746,098. Although these prior on-off sprinkler heads desirably function to stop water flow after extinguishment of a fire, they exhibit either collectively or individually various deficiences such as unreliability, temperature insensitivity, water leakage through movable seals when in a closed condition, requirements for transversely oriented inlet and outlet orifices, etc.
The object of this invention, therefore, is to provide an improved on-off sprinkler head for use in fire extinguishing systems.